Just to be honest, is there anyone saw a JS-2 as often as a tiger? Because it's too good and soviet players want challenge themselves without It or it just can't get the job done?
There's 4 commanders with the Tiger tank and only 2 with the IS2. One of them having no Shocks/Guards/PPSh units/abilities that are fairly popular currently.
In contrast out of the 4 Tiger commanders, Mechanized Assault, Spearhead and Assault Support are fairly popular commanders.
With that in mind I would be quite surprised if I saw an IS2 even half as much as the Tiger.